1. Technical Field of the Invention
The present invention generally relates to distribution of video signals via distributive optical networks such as, e.g., passive optical networks (“PONs”). More particularly, and not by way of any limitation, the present invention is directed to system and method providing video overlay using packetized video over gigabit Ethernet in such optical networks.
2. Description of Related Art
In today's access market, service providers have greater opportunities for revenue generation than ever before. Residential consumers are purchasing increasing amounts of communications and home entertainment services. Broadband communications services, such as video, form an increasingly important part of the package of services being offered by service providers to end-users. Accordingly, access network architectures are being optimized to provide cost-effective solutions for delivering a “triple play” (voice/data/video) package of services over a single, converged access network.
A passive optical network (“PON”) is a system that brings optical fiber cabling and signals all or most of the way to an end-user in residential and small business networks. Depending on where the PON terminates, the system can be described as fiber-to-the-curb (“FTTC”), fiber-to-the-building (“FTTB”), fiber-to-the-cabinet (“FTTCab”), or fiber-to-the-home (“FTTH”). PONs utilize light of different colors, or wavelengths, over optical fibers to transmit large amounts of information between end-users and network/service providers. “Passive” simply means that the optical transmission has no power requirements or active electronic devices once the signal is being transported in the network. With PONs, signals are carried by lasers and sent to their appropriate destination by devices that function much like highway interchanges, without the need for any electrical power, thereby eliminating expensive powered equipment between the provider and the customer. PONs offer customers video applications, high-speed Internet access, multimedia, and other high-bandwidth capabilities, along with traditional voice (or POTS) services.
Advantages of optical technology are speed, flexibility, and lower maintenance. Because PON is independent from bit rates, signal format, and protocols, only the equipment needed for delivering the specific services needs to be added at the ends of the network when the time comes to add new services to existing customers or to add new customers. Moreover, services can be mixed or upgraded cost-effectively as required.
Three PON networking methodologies are or soon will be standardized. These include ITU broadband PON (“BPON”), ITU Giga PON (“GPON”), and IEEE Ethernet PON (“EPON”). Both of the ITU PON standards define a WDM channel for use as an optical video broadcast signal. The IEEE EPON standard does not explicitly define such a channel, but tacitly allows such a video overlay to be used. It should be understood that although xPON-type distributive networks will be described in the present patent application, such arrangements are merely exemplary rather than restrictive or limiting with respect to the embodiments of the invention set forth in detail hereinbelow.
FIG. 1 illustrates a block diagram of an example of a prior art communications network 100. In the network 100, one or more video laser modulators (“VLMs”), such as the VLM 106, uses the derived video signal to modulate a 1550 nm optical laser. The resultant optical signal is output from the video head end 104 to a central office (“CO”) 108. A highly-linear optical amplifier (“OA”) stage 109, which may be implemented using erbium-doped fiber amplifiers (“EDFAs”), at the CO 108 amplifies the optical signal to approximately +17 dBm.
Internet data and voice signals from a network 110 are converted to optical signals in the 1490 nm band by an optical line terminal (“OLT”) 112. The signals output from the OLT 112 and the OA stage 109 are combined via a wavelength division multiplexer 114 and delivered to a PON 116 on a feeder fiber 118. In general, a PON provides a physical point-to-multipoint fiber connection. In one embodiment, the PON 116 is implemented using a glass splitter 120, which splits the combined signal received on the feeder fiber 118 into 32 distribution/drops for delivery to one of a plurality of optical network terminals (“ONTs”), such as the ONT 122, at a subscriber premises 124. At the ONT 122, the combined signal is terminated and delivered to the subscriber as analog voice, Internet Data (generally, either Ethernet or xDSL), and video (RF over coaxial cable). Traffic in the upstream direction (from the subscriber premises 124 to the CO 108) is carried in the 1310 nm optical band and is only directed toward the OLT 112 and does not reach the video head end 104, unless it is so directed over the data network 110.
FIG. 2 illustrates a block diagram of the current architecture of the ONT 122 of FIG. 1. As shown in FIG. 2, the ONT includes a triplexer 200 that converts optical signals sent via three wavelengths into electronic signals, a broadband PON transmission convergence (“PON TC”) device 204 that is equivalent to a media-access-control layer, and an ATM processor 206 that processes packetized voice into analog voice. The triplexer 200 comprises a highly-linear analog PIN photodiode for outputting RF video signals to an RF video amplifier 208. The video signals are output from the ONT 122 on a coaxial F connector. Similarly, the triplexer 200 comprises a PIN-TIA photodiode for outputting digitized data and voice signals to the PON-TC device 204. The digitized data and voice signals are then output to the ATM processor 206, which outputs the analog voice signals to POTS equipment 212 and outputs digitized data signals to an Ethernet media access control/physical access layer (“MAC/PHY”) 214.
The nature of the quality parameters of the video signal at the ONT 122 requires a significant minimum optical input level (typically −6 dBm or better). This is on the order of 25 dBm higher than that of the data signal. This disparity results in challenges in signal isolation at the optical level. Additionally, the PIN photodiode in the ONT 122 is required to be highly linear, which is both difficult to fabricate and relatively expensive. Lastly, as a result of the high optical input levels required at the ONT 122, significant optical “boosting” by OAs, in the form of EDFAs, is required along the path to maintain the level of the video signal at +17 dBm. Such OAs are significantly expensive, even when their cost is extrapolated over a multi-user PON.
An in-band video distribution scheme in which packetized video data is transmitted inband with the data and voice services is promising, but has practical, real world limitations in the form of the level of processing power required by all elements in the video path (i.e., the OLT 112 and the ONT 122), which are often internally bandwidth-limited. This results in either a limitation as to the number of video channels that can be carried or selection schemes that add to the complexity.
Therefore, what is needed is a technique and architecture for delivering low-cost broadcast IP video to a large number of users.